The present invention relates to the field of pump devices for pumping fuel from a motor vehicle tank.
More precisely, the present invention relates to the field of devices for pumping gas oil.
Numerous pump devices have already been proposed for this purpose.
As shown diagrammatically in accompanying FIG. 1, most pump devices proposed in this way comprise an electric pump 10 whose intake is provided with a filter or xe2x80x9cstrainerxe2x80x9d 20. The function of the filter is to protect the pump 10 from contamination that could clog it or give rise to other damage. Typically, but in non-limiting manner, the mesh size of the filter 20 is about 70 xcexcm. The intake of the pump 10 and the strainer can be situated directly in the main fuel tank, close to the bottom thereof, or in a reserve which is itself placed close to the bottom of the main tank and which is, for example, fed by an outlet stage from the pump or by the returned fuel that is not used by the engine.
It is known that below some specific temperature, gas oil tends to produce particles of paraffin wax.
Thus, in cold weather, and at least when starting, the gas oil can clog the filter 20 with wax, thereby preventing the pump 10 from being fed and consequently paralyzing the vehicle.
In an attempt to eliminate that major drawback, proposals have been made to increase the mesh size of the filter 20 so as to reduce the risk of it clogging, e.g. by using a filter 20 having a mesh with a mean dimension of about 200 xcexcm. Nevertheless, that proposal does not always give satisfaction, since the pump 10 is not always fully protected when using such a large-mesh filter.
Thus, at present, most fuel feed systems that use gas oil are fitted with means suitable for heating the gas oil so as to avoid clogging the fine filter that protects the high pressure pump.
However, practical implementation of that concept gives rise to difficulties. These difficulties are due in particular to the fact that the composition of gas oils made available to users can vary from one supplier to another and above all from one country to another, given that requirements concerning additives and/or refining are still not subject to international standardization.
As a result, the reference temperature at which it is desirable to put the above-mentioned heater means into operation can depend on the composition of the gas oil contained in the tank, and more commonly on the country in which the tank was filled. By way of example, this temperature is typically about xe2x88x9230xc2x0 C. to xe2x88x9240xc2x0 C. in Sweden and about 0xc2x0 C. in Africa.
Attempts have already been made to solve this problem by proposing an adjustable thermostat for triggering the heater means.
However that solution does not give complete satisfaction. Firstly it is difficult to adjust such a thermostat. Secondly, and above all, that solution theoretically requires the thermostat to be reset with each change in the composition of the gas oil put into the tank.
In addition, such heater means consume a non-negligible quantity of electrical power if they are powered continuously independently of temperature.
Document EP-A-661440 describes a fuel pump device comprising two filters associated with a pump intake. The first filter-forming strainer is placed in a main tank. The second filter is placed in a reserve bowl. The outlets from the two filters are connected to a common suction chamber by means of ducts. In addition, the second filter is fitted with a valve constituted by a seat associated with a shutter member. In the event of the two filters becoming clogged, the resulting suction causes the valve to open so that the pump sucks directly into the bowl.
The COMBEST document xe2x80x9cAutomotive fuel filtration trendsxe2x80x9d, Automotive engineering, vol. 99, no. 9, September 1991, describes various fuel filter structures.
Documents U.S. Pat. No. 3,773,144, U.S. Pat. No. 4,129,503, and U.S. Pat. No. 1,568,796 describe suction systems for tanks comprising a filter fitted with a valve adapted to be opened in the event of the filter becoming clogged.
The present invention now has the object of proposing novel pump means for gas oil that enable the above-specified drawbacks to be eliminated.
In the context of the present invention, this object is achieved by means of a gas oil pump device comprising a pump, a filtering strainer placed at the intake of the pump, and a valve disposed in a passage formed through the strainer so as to cover said passage in normal operation, the valve being adapted to open automatically when the pressure difference between the outside of the strainer and the inside thereof exceeds a threshold because of the strainer becoming clogged, the device being characterized in that the seat of the valve is angular and projects into the inside of the cage of the valve.
As explained below, the valve is preferably constituted by a fuel-proof flap. Thus, it closes the passage formed through the strainer when in the closed position. However, in a variant, the valve can be formed at least in part by a filter element possessing a mesh size equal to that of the strainer, for example.
The strainer preferably has a mesh size of about 70 xcexcm.
The valve is preferably protected by an auxiliary filter having a larger mesh size, e.g. about 200 xcexcm to 300 xcexcm. However, in a variant, the auxiliary filter can be placed at the intake of the pump and not upstream from the valve.
The present invention also provides a fuel tank fitted in this way.